1. Field of the Invention
The present invention relates to a position detecting apparatus used for an automatic focusing (auto-focusing) mechanism or the like.
2. Description of the Prior Art
Accurate and quick position detection is indispensable for an auto-focusing mechanism. Among a variety of conventional position detecting apparatus used for the focusing operation, typical ones are based on the use of a light spot or the contrast of an image.
The former apparatus using a light spot has its measuring light beam dispersed by a rough or corrugated work surface, and therefore the accurate position detection is difficult when a workpiece has a poor surface condition.
The latter apparatus using the contrast of an image operates to project a stripe pattern onto the work surface and detect the contrast of the image by means of a photodiode array or CCD camera. The apparatus is designed to process the image signal of the projected stripe pattern while varying the distance between the workpiece and the optical device, e.g., microscope, thereby implementing the position detecting and focusing operations. This apparatus has a drawback of an extended measurement time before the system is finally brought in focus.